by Michael Winter, USA TODAY

by Michael Winter, USA TODAY

The U.S. Justice Department on Monday charged 18 current or former Los Angeles County sheriff's deputies with federal civil rights violations in connection with an FBI investigation into alleged excessive force in the nation largest jail system.

The charges include unjustified beatings of inmates and visitors at downtown jails, unjustified detentions and conspiring to obstruct the investigation at the Men's Central Jail.

"These incidents did not take place in a vacuum - in fact, they demonstrated behavior that had become institutionalized," U.S. Attorney Andre Birotte Jr. said at an afternoon news conference. "The pattern of activity alleged in the obstruction of justice case shows how some members of the Sheriff's Department considered themselves to be above the law."

All are lower to mid-ranking deputies, an unidentified law enforcement official told the Associated Press.

Seventeen defendants were in custody, according to court records. They were to be arraigned later Monday.

The sheriff's department said it had cooperated with the investigation. Sheriff Lee Baca was to issue a statement later Monday afternoon.

The charges cover five cases of alleged inmate abuse, corruption and illegal arrests, and "demonstrated behavior that had become institutionalized," Birotte said in an accompanying statement.

"The pattern of activity alleged in the obstruction of justice case shows how some members of the Sheriff's Department considered themselves to be above the law," he said. "Instead of cooperating with the federal investigation to ensure that corrupt law enforcement officers would be brought to justice, the defendants in this case are accused of taking affirmative steps designed to ensure that light would not shine on illegal conduct that violated basic constitutional rights."

In once case, deputies allegedly moved a jailed FBI informant to possibly derail the investigation, AP's source reported.

The FBI has been investigating the county jail system since at least 2011.

The American Civil Liberties Union sued the Sheriff's Department in 2012 and released a report documenting more than 70 cases of misconduct.

In November, the country created a new office of inspector general to oversee the sheriff's department.

While acknowledging mistakes by deputies, Baca has defended the department and tried to distance himself from the allegations of brutality. A new database tracks inmate complaints, and he has reshuffled his command staff and hired a new official to oversee custody.